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Anti-Forensic Techniques

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Timestamps

An attacker may be interested in changing the timestamps of files to avoid being detected. It's possible to find the timestamps inside the MFT in attributes $STANDARD_INFORMATION __ and __ $FILE_NAME.

Both attributes have 4 timestamps: Modification, access, creation, and MFT registry modification (MACE or MACB).

Windows explorer and other tools show the information from $STANDARD_INFORMATION.

TimeStomp - Anti-forensic Tool

This tool modifies the timestamp information inside $STANDARD_INFORMATION but not the information inside $FILE_NAME. Therefore, it's possible to identify suspicious activity.

Usnjrnl

The USN Journal (Update Sequence Number Journal) is a feature of the NTFS (Windows NT file system) that keeps track of volume changes. The UsnJrnl2Csv tool allows for the examination of these changes.

The previous image is the output shown by the tool where it can be observed that some changes were performed to the file.

$LogFile

All metadata changes to a file system are logged in a process known as write-ahead logging. The logged metadata is kept in a file named **$LogFile**, located in the root directory of an NTFS file system. Tools such as LogFileParser can be used to parse this file and identify changes.

Again, in the output of the tool it's possible to see that some changes were performed.

Using the same tool it's possible to identify to which time the timestamps were modified:

  • CTIME: File's creation time

  • ATIME: File's modification time

  • MTIME: File's MFT registry modification

  • RTIME: File's access time

$STANDARD_INFORMATION and $FILE_NAME comparison

Another way to identify suspicious modified files would be to compare the time on both attributes looking for mismatches.

Nanoseconds

NTFS timestamps have a precision of 100 nanoseconds. Then, finding files with timestamps like 2010-10-10 10:10:00.000:0000 is very suspicious.

SetMace - Anti-forensic Tool

This tool can modify both attributes $STARNDAR_INFORMATION and $FILE_NAME. However, from Windows Vista, it's necessary for a live OS to modify this information.

Data Hiding

NFTS uses a cluster and the minimum information size. That means that if a file occupies uses and cluster and a half, the reminding half is never going to be used until the file is deleted. Then, it's possible to hide data in this slack space.

There are tools like slacker that allow hiding data in this "hidden" space. However, an analysis of the $logfile and $usnjrnl can show that some data was added:

Then, it's possible to retrieve the slack space using tools like FTK Imager. Note that this kind of tool can save the content obfuscated or even encrypted.

UsbKill

This is a tool that will turn off the computer if any change in the USB ports is detected. A way to discover this would be to inspect the running processes and review each python script running.

Live Linux Distributions

These distros are executed inside the RAM memory. The only way to detect them is in case the NTFS file-system is mounted with write permissions. If it's mounted just with read permissions it won't be possible to detect the intrusion.

Secure Deletion

https://github.com/Claudio-C/awesome-data-sanitization

Windows Configuration

It's possible to disable several windows logging methods to make the forensics investigation much harder.

Disable Timestamps - UserAssist

This is a registry key that maintains dates and hours when each executable was run by the user.

Disabling UserAssist requires two steps:

  1. Set two registry keys, HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Start_TrackProgs and HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Start_TrackEnabled, both to zero in order to signal that we want UserAssist disabled.

  2. Clear your registry subtrees that look like HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\UserAssist\<hash>.

Disable Timestamps - Prefetch

This will save information about the applications executed with the goal of improving the performance of the Windows system. However, this can also be useful for forensics practices.

  • Execute regedit

  • Select the file path HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SessionManager\Memory Management\PrefetchParameters

  • Right-click on both EnablePrefetcher and EnableSuperfetch

  • Select Modify on each of these to change the value from 1 (or 3) to 0

  • Restart

Disable Timestamps - Last Access Time

Whenever a folder is opened from an NTFS volume on a Windows NT server, the system takes the time to update a timestamp field on each listed folder, called the last access time. On a heavily used NTFS volume, this can affect performance.

  1. Open the Registry Editor (Regedit.exe).

  2. Browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem.

  3. Look for NtfsDisableLastAccessUpdate. If it doesn’t exist, add this DWORD and set its value to 1, which will disable the process.

  4. Close the Registry Editor, and reboot the server.

Delete USB History

All the USB Device Entries are stored in Windows Registry Under the USBSTOR registry key that contains sub keys which are created whenever you plug a USB Device into your PC or Laptop. You can find this key here HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\USBSTOR. Deleting this you will delete the USB history. You may also use the tool USBDeview to be sure you have deleted them (and to delete them).

Another file that saves information about the USBs is the file setupapi.dev.log inside C:\Windows\INF. This should also be deleted.

Disable Shadow Copies

List shadow copies with vssadmin list shadowstorage Delete them running vssadmin delete shadow

You can also delete them via GUI following the steps proposed in https://www.ubackup.com/windows-10/how-to-delete-shadow-copies-windows-10-5740.html

To disable shadow copies steps from here:

  1. Open the Services program by typing "services" into the text search box after clicking the Windows start button.

  2. From the list, find "Volume Shadow Copy", select it, and then access Properties by right-clicking.

  3. Choose Disabled from the "Startup type" drop-down menu, and then confirm the change by clicking Apply and OK.

It's also possible to modify the configuration of which files are going to be copied in the shadow copy in the registry HKLM\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot

Overwrite deleted files

  • You can use a Windows tool: cipher /w:C This will indicate cipher to remove any data from the available unused disk space inside the C drive.

  • You can also use tools like Eraser

Delete Windows event logs

  • Windows + R --> eventvwr.msc --> Expand "Windows Logs" --> Right click each category and select "Clear Log"

  • for /F "tokens=*" %1 in ('wevtutil.exe el') DO wevtutil.exe cl "%1"

  • Get-EventLog -LogName * | ForEach { Clear-EventLog $_.Log }

Disable Windows event logs

  • reg add 'HKLM\SYSTEM\CurrentControlSet\Services\eventlog' /v Start /t REG_DWORD /d 4 /f

  • Inside the services section disable the service "Windows Event Log"

  • WEvtUtil.exec clear-log or WEvtUtil.exe cl

Disable $UsnJrnl

  • fsutil usn deletejournal /d c:

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